An open type disposable diaper is well known that includes a liquid pervious face sheet, a liquid impervious back sheet and an absorbent body disposed therebetween and is worn by fastening fastening tapes disposed at edges on both sides of a back side to a fastening portion disposed at a predetermined position on a front side is well known.
A disposable diaper of this kind adopts, as a fastening mechanism, a hook and loop fastener mechanism where an entirety or a part of a fastening tape is made into a hook member of a hook and loop fastener, at a predetermined position of a front side waist portion, over a width direction, a loop member sheet is bonded to form an engagement section, and the hook member is pressed and engaged with the loop member that is an engagement section to fasten.
Recently, another open type disposable diaper has also been known that adopts a hook and loop fastener mechanism called a target tape-less where, without forming an engagement section by bonding a loop sheet, an external surface side of a back sheet is formed of a nonwoven sheet and a front side waist portion of the back sheet is embossed over a width direction to render the back sheet itself an engagement section is also known.
A disposable diaper that adopts a hook and loop fastener mechanism like this, even after repetition of fastening and loosing at wearing, does hardly deteriorate in the engagement force and is fastened with appropriate shearing force to be excellent in wearing feeling.
On the other hand, in a disposable diaper that adopts a hook and loop fastener of the kind, it is general that, in order to respond to a movement of a wearer, the elasticity is imparted to a flap to which a fastening tape is bonded, the fastening tape per se is imparted with the elasticity, or an engagement section-forming region is provided with the elasticity to give the elasticity to a waist-encircling portion to form so that a wearer may move easily. Furthermore, without positively imparting the elasticity like this, owing to the elongation and the like of a constituting sheet material accompanying a movement of a wearer, a waist-encircling portion is expanded and contracted not a little.
However, an engagement section of an existing disposable diaper is formed so that the separation strength off a hook member does not vary depending on a region. Accordingly, when, for example, a fastening tape is engaged by pulling toward a center portion so as to wear slightly tight, the contraction force or the like of the fastening tape works stronger to be likely to come off. On the contrary, when a fastening tape is engaged with a position close to a side portion so as to wear slightly loose, the contraction force of the fastening tape does hardly work to result in engaging at unnecessary strength.
In the configuration, in order to keep an engagement state necessary and sufficient in a state where a waist-encircling portion is stretched, there remains only whether the separation strength between the fastening type and a loop member sheet and an embossed region, which constitute an engagement section, is constituted stronger or a fastening tape or a side flap is constituted stretchy to loosen the stretching force of a waist-encircling portion. However, in an aspect where the separation strength is made stronger, a fastening tape is difficult to repeat to fasten again to be less in advantage of a hook and loop fastener. On the contrary, when the stretching force of a waist-encircling portion is made weaker, front and back body parts tend to be displaced to cause leakage.
Furthermore, depending on, for example, a shape of a waist-encircling portion due to age of a wearer or frequent movements such as rolling-over or the like, the front and back body parts frequently cause displacement. At that time, the fastening tape is frequently peeled toward a product length direction. Accordingly, at that time, a displacement width of the front and back body parts is larger in edges on both sides in a width direction than in a center portion in a width direction of a product, accordingly, one where edges on both sides in a width direction are more difficult to peel than a center portion in a width direction of a product is desired.
Now, a hook and loop fastener is an engagement member where a loop member sheet having loop elements obtained by forming a fiber in loop or in arch and a hook member sheet having a napped hook element having a swelling head shape such as a hook shape or a mushroom shape that engages with the loop elements are pressed and engaged to allow exerting adhesive force. The hook and loop fastener is, being easy to fasten and loose and having appropriate engagement force, as mentioned above, as a fastening member or the like of a disposable diaper and the like, used in a variety of fields.
Conventionally, the loop member sheet of the hook and loop fastener has been formed by enhancing loops and the like by making use of needle punch, spun bond, spun lace or thermal contraction to a nonwoven fabric that uses a fiber of a synthetic resin such as nylon, polyester or the like.
In a loop member sheet containing such a synthetic resin fiber, in order to control the engagement force and to inhibit fibers from napping, by passing through a heated pattern roll or an embossing roll, a loop element is partially fused.
However, a loop member sheet where a loop element is partially fused to control the engagement force like this is hardened in a fused portion. Accordingly, when the loop sheet like this is used in an article that comes into contact with skin such as a disposable diaper, there is unfavorable stiff feeling. Furthermore, since a heat source is necessary to produce, much energy is consumed to be high in the production cost.
Furthermore, when a design is altered, a roll pattern has to be changed, accordingly, a design change is disadvantageously difficult to apply.
Still furthermore, when a fusing treatment is once applied, the engagement force is not restored thereafter, accordingly, it is impossible to design so that the engagement force may be restrained only when it is unnecessary to engage.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 3490608    Patent Document 2: JP-A No. 09-317